my daughter wants to buy a car on finance as she has no credit history, the garage said that they would need a gurantor,her father said that he would do this,which is fine but he has a poor credit history would that stop my daughter getting the finance she needs to buy the car?
Possibly - the whole point of a guarantor is so that they can pay the finance if your daughter does a runner. If her father has a poor credit history then he is unlikely to be able to pay (in the eyes of the finance company at least) and may not be accepted by them.
It will also create a 'financial relationship' between you and your daughter on her credit file. Being associated with your poor credit history won't help her in the future.